1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head having at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, a recording head incorporates: a medium facing surface (air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other on a side of the medium facing surface, with the recording gap layer disposed in between, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve such a structure.
With decreasing track width, it becomes harder to generate a high-density magnetic flux between the two magnetic pole portions that are opposed to each other with the recording gap layer in between. On that account, it is desirable that the magnetic pole portions be made of a magnetic material having a higher saturation flux density.
As the frequency of recording signals is made higher to increase the recording density, a higher speed of change of magnetic flux, or equivalently, a reduction in flux rise time, is required of recording heads. Furthermore, less degradation in the recording characteristics of the recording heads such as overwrite property and non-linear transition shift are required at higher frequency bands. To meet those requirements, it is desirable to reduce a yoke length. Decreasing the winding pitch of the thin-film coil is effective for reducing the yoke length.
One of known techniques for decreasing the winding pitch of a thin-film coil is to form a recess in the bottom pole layer so as to place the thin-film coil in the recess, as disclosed in U.S. Pat. No. 6,043,959 and Published Unexamined Japanese Patent Application (KOKAI) No. 2001-76316, for example.
According to the method of manufacturing a thin-film magnetic head described in U.S. Pat. No. 6,043,959, the bottom pole layer, the top pole layer, and the thin-film coil are formed through the following steps. Initially, the bottom pole layer patterned into a predetermined shape is formed. The recording gap layer and a magnetic layer are then formed on the bottom pole layer in succession. Part of the magnetic layer is coupled to the bottom pole layer. Then, a mask is formed to cover portions of the magnetic layer where to form the magnetic pole portion of the top pole layer and where to form a coupling portion of the top pole layer to be coupled to the bottom pole layer. The magnetic layer, the recording gap layer and the bottom pole layer are etched by using this mask. The magnetic layer thus etched makes a pole portion layer that is to be the magnetic pole portion of the top pole layer, and a coupling layer that is to be the coupling portion mentioned above. The above-mentioned etching also forms a trim structure, in which sidewalls of the magnetic pole portion of the top pole layer, the recording gap layer and at least part of the bottom pole layer are formed vertically in a self-aligned manner. The etching also provides the bottom pole layer with a recess in which the thin-film coil is to be placed. An insulating film is then formed all over, and thereafter, the thin-film coil is formed by plating on the insulating film inside the recess. Then, a thick insulating layer is formed all over and the top surface of this insulating layer is flattened to expose the pole portion layer and the coupling layer of the top pole layer. On the flattened surface, a yoke portion layer of the top pole layer is formed so that the pole portion layer and the coupling layer are coupled to each other.
According to the method of manufacturing a thin-film magnetic head described in Published Unexamined Japanese Patent Application (KOKAI) No. 2001-76316, the bottom pole layer, the top pole layer, and the thin-film coil are formed through the following steps. Initially, a first part of the bottom pole layer patterned into a predetermined shape is formed. Next, a second part to be the magnetic pole portion of the bottom pole layer and a third part to be coupled to the top pole layer are formed on the first part. The first, second and third parts makes up the bottom pole layer having a recess in which the thin-film coil is to be placed. An insulating film is then formed all over, and thereafter, the thin-film coil is formed by plating on the insulating film inside the recess. Then, a thick insulating layer is formed all over, and the top surface of this insulating layer is flattened to expose the second and third parts. The recording gap layer is formed on the flattened surface. In the recording gap layer, a contact hole is formed at a portion thereof located on the third part. Then, the top pole layer is formed on the recording gap layer. The top pole layer is connected to the third part through the contact hole. Using the magnetic pole portion of the top pole layer as a mask, the bottom pole layer and the recording gap layer are etched to form a trim structure.
In the methods of forming a thin-film magnetic head described in U.S. Pat. No. 6,043,959 and Published Unexamined Japanese Patent Application (KOKAI) No. 2001-76316, the bottom pole layer is first patterned to have a recess therein, and thereafter the thin-film coil is formed in the recess. The thin-film coil is formed by frame plating through the following steps. Initially, a photoresist frame is formed by photolithography. Then, a thin electrode film is formed to cover this frame. With an electric current passed through this electrode film, the thin-film coil is formed by electroplating. In the case of forming the thin-film coil by frame plating, a fine frame is required to attain a smaller winging pitch of the thin-film coil.
To form the thin-film coil in the recess of the bottom pole layer as described above, the frame must be formed on the uneven bottom pole layer. However, it is difficult to form a fine frame on such an uneven base by photolithography. The reason for this is that rays of light used for exposure of photolithography are reflected off the electrode film lying on the sidewalls of the recess. The photoresist is exposed to the reflected rays as well, which makes it difficult to form a fine frame with precision. Consequently, for example, if a thin-film coil having a line width of winding of 0.3 μm or less, or a winding pitch of 0.5 μm or less, and a height of 1.5 μm or more is to be formed in the recess of the bottom pole layer by the existing photolithography techniques, the yield of the thin-film coil becomes extremely low. Thus, it has been practically difficult to form such a coil.